A Class 2 transformer, as defined by the National Electric Code (NEC), is typically associated with AC-DC power supplies, but the key characteristic is its output voltage and power limitation, not necessarily the output type.
Understanding Class 2 Transformers
The designation "Class 2" refers to the output characteristics of a power supply or transformer and is defined primarily by the National Electrical Code (NEC) in the United States. The primary purpose of a Class 2 transformer is to limit the output voltage and current to levels considered safe, reducing the risk of electrical shock and fire hazards.
Here's a breakdown of key aspects:
- Output Limitations: Class 2 transformers have strict voltage and current limitations on their output. These limitations are designed to prevent dangerous levels of energy from being delivered to connected circuits.
- Safety Focus: The primary goal is safety. By limiting voltage and current, Class 2 transformers minimize the risk of electrical shock and fire.
- Application: Class 2 power supplies and transformers are commonly used in low-voltage applications like LED lighting, thermostats, and doorbells.
AC vs. DC Output
The output of a Class 2 transformer can be either Alternating Current (AC) or Direct Current (DC). While the NEC defines the output voltage and power capabilities, it doesn't mandate whether the output must be AC or DC. The reference indicates that Class 2 applies to AC-DC supplies, implying a DC output is often the case.
Therefore, while the input to a Class 2 transformer is typically AC, the output from a Class 2 power supply can be either AC or DC, depending on the specific design of the power supply. Class 2 power supplies are frequently designed with AC inputs and DC outputs.
Class II vs. Class 2
It's also important to differentiate between Class 2 (NEC standard related to output) and Class II (IEC standard related to insulation).
- Class 2 (NEC): Deals with the output voltage and power limitations for safety.
- Class II (IEC): Percolates to the power supply's construction (double insulation, no earth ground required).
Conclusion
While Class 2 transformers can be part of AC-DC power supplies, their defining characteristic is their limited output voltage and current for safety reasons, and the output itself can be either AC or DC. Often, Class 2 power supplies convert AC input to a limited DC output.
